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iter11: WRITEBACK_CHUNK_BYTES 32 -> 128 MiB

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Prediction: ~26-27 mean (regression from iter8). Confirms chunk-size
sweet spot at 32 MiB. Then move off chunk-size as a lever entirely.
This commit is contained in:
MattJackson
2026-05-17 09:21:00 -07:00
parent d39d3933f5
commit ff22385a61
1 changed files with 7 additions and 2 deletions
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src/io/writeback_file/mod.rs
+7 -2
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@@ -73,8 +73,13 @@ use std::path::Path;
use super::writeback::WritebackPipeline; use super::writeback::WritebackPipeline;
/// Granularity at which the Linux writeback pipeline issues /// Granularity at which the Linux writeback pipeline issues
/// `sync_file_range` pairs. 32 MiB best-tested with iter8 (28.7 mean). /// `sync_file_range` pairs.
const WRITEBACK_CHUNK_BYTES: u64 = 32 * 1024 * 1024; ///
/// iter11 (2026-05-17): 32 → 128 MiB. 0.21.14 tried this under Phase
/// 2.5 and reverted; with Phase 2.5 disabled (iter8 baseline) the
/// tradeoff is different. iter8 (32 MiB) = 28.7, iter9 (64 MiB) = 27.5.
/// Trying 128 to see if the iter9 dip was noise or a real trend.
const WRITEBACK_CHUNK_BYTES: u64 = 128 * 1024 * 1024;
pub(crate) struct WritebackFile { pub(crate) struct WritebackFile {
file: File, file: File,